1. Field of the Invention
The present invention relates to a curtain airbag that is inflated and deployed along a side surface of a vehicle interior for the purpose of protecting occupants during a side crash or a rollover (lateral rollover) of a vehicle.
2. Description of the Related Art
In recent years, high levels of safety performance have been required of vehicles. This trend is shared across countries around the world, where most vehicles are currently standard-equipped with airbags as vehicle safety devices. Companies involved in vehicle development have adopted ongoing safety improvements as a major development guideline. In line with this, new airbags are continually being developed.
Standards for evaluating vehicle safety differ from country to country, and companies approach product development such that products can meet evaluation standards in multiple countries. In the United States, for instance, which has the largest automobile fleet in the world, Federal Motor Vehicle Safety Standards (FMVSS) have been established by the National Highway Traffic Safety Administration (NHTSA). In the Notice of Proposed Rulemaking (NPRM, Docket Number: NHTSA-2009-0183) for FMVSS, which is the basis of FMVSS 226 established by the NHTSA, a requirement is proposed that aims at “reducing the probability of occupant ejection from a vehicle through a side window using an ejection mitigation system in the event of a side impact crash or a rollover (lateral rollover)”. The requirement can be met by providing a curtain airbag as an anti-ejection countermeasure that forms an ejection mitigation system.
A curtain airbag is an airbag that is received above a door so as to be inflated and deployed along a side window of a vehicle in the event of an impact. The curtain airbag includes a gas generating device called an inflator. The inflator supplies gas to the inside of the curtain airbag upon detecting an impact with the aid of a sensor. When the curtain airbag receives the gas, a bag-shaped inflation region is inflated to break accommodation tapes or the like with its internal pressure and is deployed into the vehicle interior while pushing a roof trim.
The inflation region of the curtain airbag is partitioned into a plurality of small rooms (chambers) for receiving the occupant. The chambers are set by taking the positions of seats, the flowability of gas, and the like into consideration. In order to improve performance of the curtain airbag in preventing the occupant from being ejected outside the vehicle, it is ideal if the chamber maintains high internal pressure, from completion of inflation and deployment, until the occupant contacts the chamber. For example, in a curtain airbag disclosed in Japanese Patent Application Publication No. 2005-178606, a gasket is formed in the inflator as a sealing member. Moreover, after the inflator is inserted in the curtain airbag, the curtain airbag is joined by bands at the position of the gasket above the base fabric of the curtain airbag. Due to this, it is possible to prevent leakage of gas and to maintain high internal pressure of the curtain airbag.
However, although the technique of Japanese Patent Application Publication No. 2005-178606 can prevent leakage of gas from the entire curtain airbag, the location where the occupant actually contacts the airbag is a portion of the chambers of the curtain airbag. For example, when the occupant contacts one chamber, the gas filled in the chamber moves to another chamber due to the weight of the occupant although the gas does not leak from the curtain airbag. As a result, the internal pressure of the chamber that the occupant contacts decreases, and it is difficult to improve the ejection preventing performance.